| Carboxylic acids have been widely used in organic synthesis, pharmaceuticals engineering, fine chemical industry and so on, particularly for chiral carboxylic acids. Traditional analytical methods such as HPLC, CE, GC and MS are usually time-consuming and quite expensive as a result of requirement for sophisticated instrumentation. Thus, it is very necessary to develop effective methods for analyze chiral carboxylic acids. Great progress has been made by the method of sensor for the advantages of simple, fast, real-time online and so forth. Among nano gold colorimetric sensor, which is characterized for simple, low cost, high-throughput and etc., is prominent in bioactive compound screening. However, it was rarely applied in the chiral recognition of organic compounds. This thesis aims to construct a new type of Au NPs colorimetric sensor to enantioselect chiral carboxylic acids.The first part is a review of the progress of chiral recognition method and nano gold sensor.The second chapter synthesized a chiral recognition molecular Schiff base and constructed a nano gold colorimetric sensor based on it and studied its pH stability. Firstly, citrate stabilized gold nanoparticles had been prepared. Following citrate stabilized gold nanoparticles was modified by the chiral recognition molecular schiff base, chiral nano gold sensor constructed. The nano gold sensor was characterized by UV-Vis absorption spectrophotometer and transmission electron microscopy(TEM) and the pH stability of nano gold sensor in the water was studied. The results showed that the nano gold sensor was stable when pH was more than 8.0 and was able to enantioselect chiral carboxylic acids in water.In the third chapter, the research explored the conditions of Au NPs sensor recognizing chiral carboxylic acid, established a model system for Au NPs sensor enantioselctive chiral carboxylic acids and examined if the nano gold sensor can ubiquitously recognize chiral carboxylic acids. It was found that when D-mandelic acid(MA) was added to nano gold sensor, gold nanoparticles were assembled and the color of the solution changed from red to blue, while when L-MA was added, the color remained same. The result indicated that the Au NPs sensor can enantioselect and visually identify chiral MA well. Then the model system of HTS assays for total acid concentration([Acid]t)and ee% was established based on MA and made out the standard curve plotting for [Acid]t and ee%, the R2 of standard curve were bigger than 0.99. Finally, the chiral nano gold sensor successfully recognized four different kinds of chiral carboxylic acids(mandelic acid, tartaric acid, malic acid and 3-phenyllactic acid), demonstrated nano gold sensor's ubiquity in recognized chiral carboxylic acids.In the fourth chapter, the mechanism of recognition was studied by computer simulation and by determining the binding constant between receptor Schiff base and ligand MA. By the classical Benesi-Hildebrand experiment, the binding constant between receptor Schiff base and MA was determined as 1: 1. The equilibrium constant K was significantly enlarged when Zn2+ was added, which indicated that Zn2+ could greatly strengthen the interaction between the receptor Schiff base and MA. Then we adopted molecular simulation to further recognize the type of association. The CDOCKER energy was used to judge the strength of interaction between receptor Schiff base and lignd MA, and the CDOCKER energy of D-MA was bigger which illustrated the interaction force with D-MA was greater, which was consistent with the results in the third chapter. Through computer simulation, we presumed there were coordination interaction, hydrogen bonding, ?-? interaction and steric effect between receptor Schiff base and MA. |
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